1. Field of the Invention
The present invention generally relates to magnetic recording media and magnetic storage apparatuses, and more particularly to a magnetic recording medium having a seed layer and an underlayer which is made of a binary alloy, and to a magnetic storage apparatus which uses such a magnetic recording medium.
2. Description of the Related Art
A typical longitudinal magnetic recording medium includes a substrate, a seed layer, a Cr or Cr alloy underlayer, a Co—Cr alloy intermediate layer, a Co alloy magnetic layer where the information is written, a C overlayer, and an organic lubricant which are stacked in this order. Substrates that are presently used include NiP-plated Al—Mg alloy substrates and glass substrates. The glass substrate is more popular due to its resistance to shock, smoothness, hardness, light weight, and minimum flutter especially at a disk edge in the case of a magnetic disk.
Al substrates with electroplated NiP has been widely used for many years for magnetic recording purposes. When grown at high temperatures Ts >150° C., Cr alloy underlayers form a desirable (002) orientation. Sputtered NiP on glass or Al substrate has proven to be as effective in promoting the proper crystallographic orientation of Cr underlayers as disclosed in a U.S. Pat. No. 5,866,227. Therefore, with the same seed layer, existing Al media technology can be used for the subsequent layers. FIGS. 1 through 3 show examples of the layer structure of the conventional magnetic recording media. In FIGS. 1 through 3, those parts which are the same are designated by the same reference numerals.
In a first example shown in FIG. 1, on a glass substrate 1 is formed an amorphous layer 3 made of NiP. The NiP layer 3 is preferably oxidized. On the NiP layer 3 is grown an underlayer made up of two essentially Cr underlayers 4 and 5 with a (002) texture on which a magnetic layer 7 is deposited. The second Cr underlayer 5 usually has a larger lattice parameter than the first Cr underlayer 4.
The magnetic layer 7 has a (11 20) crystallographic orientation, and may be made up of a single layer or multiple layers that are in direct contact and behave magnetically as one magnetic layer. An interlayer 6 made of a CoCr alloy may be disposed between the magnetic layer 7 and the Cr underlayers 4 and 5. To enhance the adhesion of NiP to glass, elements such as Cr may be alloyed with NiP or a separate adhesive layer 2 made essentially of Cr may be employed. However for metallic substrates like Al, it is not required to employ this adhesive layer 2. On the magnetic layer 7, a protective layer 8 made of C, and an organic lubricant layer 9 are deposited for use with a magnetic transducer such as a spin-valve head.
In a second example shown in FIG. 2, the structure is similar to that of FIG. 1. But in FIG. 2, the magnetic layer 7 is replaced by a plurality of layers 7-a and 7-b that are antiferromagnetically coupled through a spacer layer 10 made of Ru, so as to form a so-called synthetic ferrimagnetic medium (SFM). The first layer 7-a functions as a stabilizing layer, and the second layer 7-b functions as a main recording layer.
A third example shown in FIG. 3 utilizes a refractory metal seed layer 3-a made of Ta-M, where M is either nitrogen or oxygen. On the glass substrate 1 is formed a Ta-M seed layer 3-a either by reactive sputtering with Ar+N2 or Ar+O2 gas on which an underlayer 4 is deposited. The crystallographic orientation of (002) is mentioned in a U.S. Pat. No. 5,685,958, but the composition of the underlayer is limited to Cr or Cr alloy, and no mention is made of underlayers made of materials such as B2 structured materials, for example. The magnetic layer 7 is formed on the interlayer 6 or the underlayer 5 with a (11 20) preferred orientation as in the first example described above.
The microstructure of the magnetic layer which includes grain size, grain size distribution, preferred orientation and Cr segregation strongly affect recording characteristics of the magnetic recording medium. The microstructure of the magnetic layer is usually controlled by the use of one or more seed layers and one or more underlayers.
Usually, NiP is used as the seed layer on a suitable substrates made of glass or aluminum. Various seed layer materials such as CoCrZr, NiAl and RuAl may be used to obtain in-plane magnetization required for the longitudinal recording. The AlRu seed layer has become more popular due to its influence on the strong texture growth of the subsequent underlayers and magnetic recording layers. Also the AlRu seed layer was found to reduce grain sizes of the subsequent underlayers and the magnetic layers.
AlRu is a B2 structured material in composition ranges of 50% Ru and 50% Al. Though B2 structured AlRu is useful, it is increasingly demanding to search for other composition ranges of AlRu. One way to approach the problem is to sputter deposit from two different targets respectively purely made of Al and Ru in the same chamber, that is, to employ a multicathode system. By varying the power ratios between the two targets, it is easy to study large composition ranges which are otherwise quite expensive using various single alloy targets made of AlRu alloys.
Such a multicathode system offers new ways to search for composition ranges which give the B2 structure of AlRu. However, there can be substantial differences between the film growths when made from single alloy target and from the multicathode system. For example, when AlRu50 is used as a single alloy target, it is very easy to form, under normal sputtering parameters, a (001) texture on top of which grows Cr(002) and Co alloy magnetic layer with (11 20) texture. However, when films are deposited with Al and Ru using the multicathode system, practically it is very difficult to form a good (002) in-plane texture of AlRU50.
Accordingly, there are demands to realize alternate structures which can be used to form the (001) texture of AlRu using the multicathode system. In addition, there are also demands to extend the use of the multicathode system to other B2 structured materials which may be used to obtain the preferred (001) texture for the longitudinal magnetic recording medium.